text:
What is the thick, dashed, magenta line on a sectional chart?
In the attached area of the sectional chart we see restricted areas R-2101 and R-2102. Also covering that general area is a circular, thick, dashed magenta line. There's a notice there that I assume corresponds to it, but I wasn't familiar with this marking before I saw it. I glanced at the Aeronautical Chart User's Guide but didn't see a reference. Anyone know what's happening here?

The Atlanta sectional near KANB, KASN, and KPLR gives a hint:

FOR REASONS OF NATIONAL SECURITY
PILOTS ARE REQUESTED TO AVOID FLIGHT
AT AND BELOW 5000’ AGL IN THIS AREA

It is called a National Security Area, which FAA’s training ALC-42: Airspace, Special Use Airspace and TFRs describes as follows.

National Security Areas
National Security Areas consist of airspace of defined vertical and lateral dimensions established at locations where there is a requirement for increased security and safety of ground facilities. Pilots are requested to voluntarily avoid flying through the depicted NSA. When it is necessary to provide a greater level of security and safety, flight in NSAs may be temporarily prohibited by regulation under the provisions of 14 CFR Section 99.7. Regulatory prohibitions will be issued by System Operations, System Operations Airspace and AIM Office, Airspace and Rules, and disseminated via NOTAM. Inquiries about NSAs Inquiries should be directed to Airspace and Rules.
Example — National Security Area near Pueblo, Co. and request to avoid flight at and below 3000’ AGL.

Wikipedia gives a brief description.

In United States aviation, a National Security Area is a designated airspace through which flight is discouraged for reasons of national security.
Flight through NSAs is not prohibited and no special advance clearance or authorization need be obtained to enter them. However, pilots of aircraft are strongly encouraged to either stay clear of NSAs or obtain prior authorization to pass through them in order to reassure the controlling agency that no threat to national security exists.
NSAs are a compromise between normal airspace and restricted or prohibited airspace. NSAs can be temporarily converted into restricted airspace by NOTAMs.
On VFR sectional charts, NSAs are delimited by a heavy dashed magenta border and a special notation.

The thick dashed magenta line indicates a National Security Area.

National Security Areas indicated with a broken magenta line national security area dashes and Special Flight Rules Areas (SFRAs) indicated with the following symbol: sfras , consist of airspace with defined vertical and lateral dimensions established at locations where there is a requirement for increased security and safety of ground facilities. Pilots should avoid flying through these depicted areas. When necessary, flight may be temporarily prohibited.

The answer is in the Aeronautical Chart User's Guide, I just initially overlooked it.

National Security Area.

(source)

Apparently there are "National Security Areas" which are marked with a dashed magenta line. Here is the description from the guide:

National Security Areas indicated with a broken magenta line and
  Special Flight Rules Areas (SFRAs) indicated with the following
  symbol: , consist of airspace with defined vertical and lateral
  dimensions established at locations where there is a requirement for
  increased security and safety of ground facilities. Pilots should
  avoid flying through these depicted areas. When necessary, flight may
  be temporarily prohibited.

Sounds reasonable, but I was asking for the sake of utilizing the chart in general, not in a way specific to this area. This might make a better comment.

@RyanBurnette I updated my answer with more details.

I am familiar with both restricted and prohibited areas. The thick dashed line I'm referring to is neither.

The "R-2101" marking seems to be pointing at the blue hatched area nearby, not the red circle. R-2102 is the larger hatched area above it.

Hmm, right, I have updated my answer, apparently it is a "National Security Area" which means they have alien bodies there or something.

Yea I found it in the guide too. I can't find something like this until I've bothered to post it as a question on SE. ;)

@TylerDurden It basically means "we don't want anyone ramming a plane into anything here or taking photographs too closely," though, of course, nowadays, you could take excellent photographs from 3,000' (or 5,000' as the case may be.) The nuclear research facility close to where I live has one of these, for example.


text:
Does my 1st class medical give me 2nd and 3rd class medical privileges after it expires?
If a 35 year-old pilot were issued a 1st class medical on January 15, 2012, am I correct that that pilot would be able to exercise privileges requiring a 1st class medical until January 15, 2013? Or would they extend until January 31, 2013? The chart in 14 CFR 61.23 mentions something about it expiring on the last day, but I can't find that exact language anywhere but in the header row of the reference table.
Additionally, after the 1st class medical certificate expires, does it not afford the pilot the privileges of a 2nd class medical for the 60 months listed in 14 CFR 61.23? I'm looking for the part of the FAR that explains how medical certificates of a higher class afford the privileges of a lower class after their original designation period expires.

A first class medical issued to a 35 year old pilot on 15 Jan 2012 will let that pilot:

exercise privileges of an ATP certificate until 23:59 31 Jan 2013
exercise privileges of a commercial certificate until 23:59 31 Jan 2013
exercise privileges of a private, recreational, student or CFI certificate (if the CFI is acting PIC) until 23:59 31 Jan 2017

Your first class medical is always a first class medical -- you don't get private pilot privileges for 5 years because a first class medical grants third class privileges, rather you get private pilot privileges for 5 years because that is what a first class medical grants you.
These durations are from the table of 61.23 (d).  You don't see this language in the text above the table because they are not concerned with the duration of the privileges but only the minimum required medical class for specific operations.
For example, 61.23 (a)(2)(ii) says you must hold at least a second class medical to exercise the privileges of a commercial certificate and 61.23(d)(1)(iii) and 61.23(d)(2)(i) list the duration that each of an first and second class medical can be used to for this purpose.

I especially appreciate your point about a first class medical always being a first class medical, but the specificity about the times on privileges. Thanks, it clarified everything that I wanted to make sure I understood clearly.

I'm a bit unsure what you're looking for, because the answers to your questions are all in the table that you already found. But anyway, the medical would expire for first-class use on Jan 31 2013. The language is in the table header, as you already noted (my emphasis):

Then your medical certificate expires, for that operation, at the end
  of the last day of the 12th month after the month of the date of examination shown on the medical certificate

For second-class privileges - by which I assume you mean commercial pilot privileges - the medical would also expire on Jan 31 2013, as per the third row in the table, which covers these privileges:

a commercial pilot certificate or an air traffic control tower
  operator certificate

The only way you can use it for 60 months is for the following privileges:

a recreational pilot certificate, a private pilot certificate, a
  flight instructor certificate (when acting as pilot in command or a
  required pilot flight crewmember in operations other than glider or
  balloon), a student pilot certificate, or a sport pilot certificate
  (when not using a U.S. driver's license as medical qualification)

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text:
What steps can pilots take to mitigate the risk of controlled flight into terrain (CFIT)?
One of the inherent risks in flying an aircraft is a controlled flight into terrain (CFIT) incident. CFIT occurs when a flight impacts terrain while under positive control. Aside from incidents of suicide, this means the terrain impact came as a surprise to the pilot.
Controlled Flight Into Terrain Awareness is a special emphasis area in the Federal Aviation Administration's (FAA) practical test standards (PTS). The FAA felt it necessary to include this as a special emphasis area because of the prevalence of this type of incident.
What steps can pilots take to mitigate the risk of CFIT?

. . . just a guess but I would think "Don't fly into the side of mountains!" would be pretty high on the list :)

Obligatory Cartoon. I know it's not an answer, but I couldn't resist!

@TomMcW The dreaded embedded cumulogranite.

There are a few things you can do to help mitigate it.
Get An Instrument Rating: Some CFIT accidents happen during a nasty mix of mountain flying, scud running and an inevitable flight into IMC, which ends with hitting the side of a mountain, an instrument rating here can be a truly valuable thing in these situations.
Plan Your Routes and Minimums Carefully: This takes place in the preflight and you should always check your charts for minimum altitudes as well as man made obstructions that may be in your flight path. Once you have your minimum altitude selected, stick to it. If weather does not permit that altitude either alter your course or scrub the flight. There is some good info from AOPA on it here.

Synthetic Vision: Apps like ForeFlight are quickly becoming common place in aviation as are glass cockpits, and these have proven invaluable in terms of terrain awareness and avoidance as many of them now include synthetic vision with terrain maps. Good preflighting is still key and you should always inform your self of all potential terrain before a flight, while technology can aid in avoidance you should always have a backup plan.
Avoid The Mountains: This is sometimes not an option but if you as the PIC feel uncomfortable you should always choose a route around terrain if possible.
Practice Mountain Flying: Just as you would with any other aspect of aviation you can always get an instructor and practice mountain flying. The FAA has some tips here but mountain flying carries its own risks and unique cases that you should be ready for. Mountains can have turbulent airflow and you should make an effort to understand how wind flows over them, you can find a discussion on it here.

Get a FIS-B Weather Receiver: As mentioned above winds can be important when flying. It's worth it to have an FIS-B weather in receiver so that you always have the most up to date information.

+1 for the "practice mountain flying" bit (though I would phrase it as "Take a mountain flying class" personally) -- A lot of the mountain-related accidents probably don't qualify as "controlled" flight into terrain as you're arguably not in control if a downdraft slams you into a ridge, but being aware of the special challenges and dangers of mountain flying could help save your life if you're flying around in the mountains.

"so that you always have the most up to date information" — remember that NEXRAD data can be significantly delayed even beyond the displayed delay time. Watch and internalize this AOPA Accident Case Study. I'm not sure if FIS-B is the same as NEXRAD or not, but be aware.

OK, so my rather flippant comment aside, avoiding controlled flight into terrain is largely an exercise in common sense (many FAA "Special Emphasis Areas" could be rolled up into a special emphasis on common sense).
It basically boils down to three things:

Knowing where the terrain / obstacles are.
Knowing where your aircraft is.
Ensuring your aircraft doesn't get too close to terrain or obstacles.

So how do we do that?

Charts and Elevation Figures
For many pilots there's a simple and practical way to do this printed right on your VFR sectional chart: The Maximum Elevation Figure (MEF):

The MEF indicates the tallest feature (terrain or obstacle) in a given quadrangle on the sectional. If you are flying with a healthy margin (500-1000 feet or more) between you and the Maximum Elevation Figure you will not hit terrain or obstacles - they will be below you.

The MEF is one reason charts expire: As new obstacles are constructed (buildings, radio towers, etc.) the MEF in each quadrangle will be updated appropriately.

ATC Information (and More Charts)
ATC deals with an altitude which is useful for all pilots to know: Minimum Instrument Altitude (MIA). This altitude provides a guaranteed obstacle/terrain clearance (1,000 feet, or 2,000 feet in designated mountainous areas) for instrument flights.
Operating at or above the Minimum Instrument Altitude for a region gives you similar protections to operating at or above the MEF altitude from the VFR sectional, and also usually ensures that ATC will have radar contact with you.
The Minimum Instrument Altitude (and another useful one, the Minimum Vectoring Altitude) are charted for center and TRACON facilities. Most pilots haven't ever seen these charts (they're "Not For Navigation" and not particularly useful unless you know the ground over which the sectors are drawn), but they are available from the FAA as supplemental information.

Aircraft Performance and Common Sense
Unfortunately some pilots don't have the option of flying over all the terrain they may have to deal with - pilots in mountainous areas have to use mountain passes to cross ridges, and may be flying between peaks that are above their altitude.
It's here that common sense and aircraft performance play into things: You know your aircraft has a given rate of climb given its current altitude and loading, and that terrain is rising at a given slope below you.  It is then the pilot's responsibility to ensure that they can out-climb the terrain, and to ensure that there is an "out" (either another pass to divert to or enough room to safely make a 180-degree turn if the terrain is out-climbing the aircraft).
This applies for man-made obstacles as well as terrain - misjudging the turning radius of your aircraft in flight can be fatal if you're relying on that to get you out of trouble.
Common sense dictates that you don't enter a pass (either a canyon/valley or a corridor surrounded by tall buildings) unless you know you can safely fly through or turn around.

Fancy Electronic Tools
Electronic flight planning applications have made terrain avoidance much easier: programs like ForeFlight and Garmin Pilot include "Hazard Advisor" and "Altitude Advisor" functions that will show where your planned route will intersect terrain or obstacles.

Many electronic flight bag / flight planning programs also include limited synthetic vision capabilities, and some glass-cockpit aircraft also include these capabilities. The virtual terrain presentation available using synthetic vision systems can be helpful if flying in IMC or marginal VFR weather:

I know nothing about piloting but 500 ft seems like an awfully small amount of clearance. Can it really be that low? I expected more like 2,000 feet...

@Mehrdad Per FAR 91.119 500 feet AGL / 500 feet from any "person, vessel, vehicle, or structure"is the absolute bare minimum for an airplane (in wide-open or sparsely-populated areas), and 1000 feet is the minimum for "congested areas". 2000 feet is a much more practical number though.

You might want to mention the OROCA as well, unlike the MEF it includes vertical clearance from terrain and obstacles. It's shown on the regular IFR en route charts.

The most important thing for the safety of any flight happens before you leave the ground, and that is planning. Know your route, have contingencies, and set limits on deviations. Set conditions on when you will abandon your plans and turn back, and stick to them regardless of peer pressure. Try making a good decision while you're being bounced around in turbulence, the visibility is rapidly worsening, and you have a bunch of people who know nothing about flying telling you to just go for it and you'll see why it is better to have a plan.
Many CFIT accidents happen because pilots fly into poor weather and elect to go on rather than turn back, which is sometimes called get-there-itis. You've flown 2 hours and the destination is only 30 minutes ahead, surely this cloud bank is only a mile or two thick and I'm instrument rated. Oops - where'd that mountain come from?! Flying through clouds is not safe without planning, even if with an instrument rating.
Other accidents happen because pilots decide to fly below weather. The weather keeps getting lower so they go lower until they are too low to avoid terrain. They didn't set a limit on how low the weather has to get before they turn back, or if they set a limit they don't stick to it because of wishful thinking or get-there-itis.
All the fancy tools in the world are no substitute for a map and good planning.

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text:
What are the common mnemonic devices used to remember equipment required by 14 CFR 91.205?
I'd like for this question's answers to be a references of the mnemonic devices pilots can use to assist with memorization of the equipment required by the FAA for flight in powered civil aircraft. What are the common mnemonic devices used to remember equipment required by 14 CFR 91.205?

For VFR Day Flights, you can use "A TOMATO FLAMES":
A - Altimeter
T - Tachometer for each engine.
O - Oil temp indicator for each engine
M - Manifold pressure gauge for each altitude engine
A - Airspeed indicator
T - Temperature gauge for each liquid cooled engine
O - Oil Pressure gauge for each engine
F - Fuel quantity gauge for each tank
L - Landing gear position lights (if retractable gear)
A - Anti-collision lights (aircraft certificated after March 11, 1996)
M - Magnetic direction indicator
E - ELT, if required by §91.207
S - Safety belts / Shoulder harnesses

For VFR Night Flights, you can use "FLAPS". This will be in addition to all the equipment required for a VFR Flight in Daylight.
F - Fuses (spare set)
L - Landing light (if for hire)
A - Anti-collision light
P - Position lights (navigation lights)
S - Source of power (such as battery)

Additionally, as @wbeard52 pointed out below, you can use "GRABCARD" as a mnemonic device to memorise the equipment required for IFR Flight. Again, these would be in addition to all the equipment required for VFR Day and Night Flight.
G - Generator/alternator
R - Radios (two way and navigational equipment
appropriate for the ground facilities to be used)
A - Altimeter (sensitive) adjustable for barometric pressure
B - Ball (slip-skid indicator, which is part of your turn coordinator)
C - Clock (shows hours minutes and seconds and installed as part of aircraft equipment)
A - Attitude indicator
R - Rate of turn indicator
D - Directional gyro (Heading indicator)

Dont forget GRABCARD for IFR flight.

@wbeard52 I specified VFR in the question figuring I'd make a separate one for IFR equipment later. Good call though.

Good enough. I'm updating the question to cover all mnemonics for 91 205.


text:
How can a CFI renew their certificate with the FAA?
I've read that there are several ways a CFI can renew their FAA instructor certificate. What ways are available for a CFI to renew?

Hi Ryan, in which jurisdiction? There is different options available per CAA.

14 CFR 61.197 lists renewal requirements for flight instructors.
If your CFI certificate is still valid (unexpired) than you can renew by any one of the following:

Getting a new rating on your CFI certificate or re-taking a practical test for an existing rating on your CFI certificate

(1) Passing a practical test for—
(i) One of the ratings listed on the current flight instructor certificate; or
(ii) An additional flight instructor rating; or

Having had at least 5 students in the last 2 years with an 80% or higher pass rate

(i) A record of training students showing that, during the preceding 24 calendar months, the flight instructor has endorsed at least 5 students for a practical test for a certificate or rating and at least 80 percent of those students passed that test on the first attempt.

Being a check pilot, chief flight instructor, check airman or flight instructor for a part 121 or 135 operation and active in pilot evaluation during the last 2 years

(ii) A record showing that, within the preceding 24 calendar months, the flight instructor has served as a company check pilot, chief flight instructor, company check airman, or flight instructor in a part 121 or part 135 operation, or in a position involving the regular evaluation of pilots.

Completing an approved refresher course within the preceding 3 months

(iii) A graduation certificate showing that, within the preceding 3 calendar months, the person has successfully completed an approved flight instructor refresher course consisting of ground training or flight training, or a combination of both.

Passing a US armed forces military instructor proficiency check in the preceding 12 months.

(iv) A record showing that, within the preceding 12 months from the month of application, the flight instructor passed an official U.S. Armed Forces military instructor pilot proficiency check.

If you are not actively instructing and just maintaining your certificate the easiest method is the approved refresher course.  There are a few weekend workshops and a online courses that are approved.  The last time I did this method I used an online course and submitted the 8710 via IACRA and completed the whole thing over a weekend and with no physical paperwork.
If your certificate has expired, even if you have completed the above but failed to submit the proper paperwork in time, then you can no longer do this the easy way and have to look at 14 CFR 61.199.  To reinstate an expired certificate you must either pass a practical test for one of your existing CFI ratings or pass a practical test for a new rating for your CFI certificate.


text:
How should operations be conducted at a towered airport that is in uncontrolled airspace?
How should operations be conducted at an airport with an operating control tower that is in Class E (controlled) or Class G (uncontrolled) airspace? Is this topic covered in an FAA publication such as the Aeronautical Information Manual (AIM) or Pilot's Handbook of Aeronautical Knowledge (PHAC)?

Airport with an operating control tower = talk to it.
From the regulations:
§91.126(d) (concerns Class G) and §91.127(c) (concerns Class E) are identical.

Communications with control towers. Unless otherwise authorized or required by ATC, no person may operate an aircraft to, from, through, or on an airport having an operational control tower unless two-way radio communications are maintained between that aircraft and the control tower. Communications must be established prior to 4 nautical miles from the airport, up to and including 2,500 feet AGL. However, if the aircraft radio fails in flight, the pilot in command may operate that aircraft and land if weather conditions are at or above basic VFR weather minimums, visual contact with the tower is maintained, and a clearance to land is received. If the aircraft radio fails while in flight under IFR, the pilot must comply with §91.185.

Treat a class E or class G tower just as you would Class D. The only differences are Basic VFR minimums, 4nm undepicted area, and IFR procedures


text:
Are directional instruments like an HSI or AHRS immune to magnetic compass error?
Pilot educational curriculum includes learning about magnetic compass errors intrinsic to their construction.
A standard magnetic compass in an airplane erroneously shows turns when accelerating or decelerating on an east or west heading. They also read incorrectly during turns from the north or the south.
My question is about more advanced instruments like a fluxgate compass found slaved to an HSI or a magnetometer used in an AHRS. Are these systems impervious to the compass errors present in a magnetic compass?

The short answer is yes, but for different reasons.
The analog HSI in most aircraft that have them either has an internal directional gyroscope, or it is slaved to the directional gyro (more often the former than the latter as the HSI often replaces the DG). An analog DG/HSI must still be periodically corrected for precession error by levelling off, letting both instruments stabilize and then adjusting the HSI's card to the magnetic compass.
AHRS systems that power glass cockpits use a solid-state directional gyro that is corrected by a magnetometer (an antenna device that directly senses the relative direction of the magnetic field) rather than a floating magnet. This makes them impervious to the types of error commonly seen in floating compasses such as acceleration bias (which causes all the behaviors you mentioned). They can still be sensitive to nearby ferrous metal structural members and to electrical currents, requiring a digital version of "spinning the compass" with corrections input into the software that uses the magnetometer readings, and magnetic declination must also be accounted for (either mentally by the pilot, manually based on declination charts or in more sophisticated systems by directly incorporating position data from the GPS).

In other industries, one would usually still use a gyro for something like an HSI, because magnetometers tend to be noisy. You can filter out the noise, but doing that makes the instrument slow (at least relative to a gyroscope). Instead the magnetometer is often best used to slowly apply automatic drift correction to a gyro's output. I would not be surprised if many/most glass cockpits actually did that (using a solid state gyro, of course).

Most of the time, magnetic declination does not have to be accounted for, because all headings are normally given in reference to magnetic north. The only exception is near the magnetic poles where true headings are used.


text:
Should time in turbojet aircraft be logged as complex?
I was having a discussion with a colleague about what aircraft qualify for logging complex time. We were discussing whether or not time flying transport-category turbojet aircraft qualified as complex according to the regulations. It's probably irrelevant at that point in a career, but my interpretation is that turbojet aircraft are not complex. 14 CFR 61.1 defines a complex aircraft as one having a retractable landing gear, flaps, and a controllable pitch propeller. It goes on to give some provisions for control computer or FADEC, but it still mentions propellor controls. In turbojet aircraft you just set the throttle, even if there are a lot of computer-controlled variables changing in the engine.
While it's not a jet, the Daher-Socata TBM 900 single-engine turboprop airplane has a single throttle quadrant and an automatically controlled propeller. It's still considered complex under the regulations even though there's no lever to adjust the prop and it's still complex. I give this example only because it has a single throttle lever and is still complex.

I'd love to get more interpretations on whether turbojet aircraft are technically complex according to the definitions of 14 CFR 61.

I'm a bit confused by your terminology: turbojets have no propellers and most modern 'jet' engines are really turbofans, which also have no propellers. Or are you asking about turboprops?

Daher-Socata TBM 900 is not a turbojet (nor turbofan), it is a turboprop. And it is unusual among turbo-props with not having a propeller control. Most turboprops do have propeller pitch levers that control the desired RPM and allow feathering the propellers.

Did I say that the TBM 900 is a turbojet?

@RyanBurnette: Well, you consistently refer to "turbojet aircraft", and then use the TBM 900 as an example.

Take one of the blank columns in your logbook and write "Turbine" in it.  Put your turbine time there.  When you can finally start logging that the only logging category that truly matters going forward is "turbine PIC".  No one is going to ask for "complex", "high performance" or "high altitude" time once you get to that stage of your career.

I have edited the title to reflect the body of the question.

@Dave: I think you made it worse.  The question does clearly seem to be asking about turbojets.  The TBM 900, which is a turboprop, is given as an analogy to suggest that maybe turbojets could still be considered complex.

I have changed it back however i interpreted the question differently I guess, my apologies.

I clarified again. The TBM example is there because it's an aircraft with a single throttle lever that is still complex.

A TBM900 IS a turbine airplane.

Yea I think I meant jet. Edited.

Complex ratings apply only to aircraft with propellers, so any kind of jet aircraft is by definition not complex.

I would add that all turbojets require type ratings so wouldn't be covered by the general category-class with endorsement system anyway.

Turboprops area complex, certainly because of the gear and flaps.
Regarding the prop, of course, some do have prop levers, but many single-engine FADEC systems have electric prop governors. In the case of 2-lever systems, like the TBM and the PC-12, there is a condition lever which does indeed control the prop, even though only in certain regimes of flight.
See What does the condition lever in turboprops control?

It's one of those arbitrary and outdated regs from the dark days of the FAA. I bet you could log it as TAA, which is now a substitute for complex as far as the commercial certificate requirements. Again not a great regulation, they could have combined the two and said aircraft with any combination of 3 or more items of this list...(Bureaucrats and fudds, whatta ya gonna do.)
I mean why can you fly a turboprop(under 12500lb) with a standard cat and class rating but all turbo-jet/fan require a type rating? A turbo-prop is far more complicated both operationally and for points of failure. When the reg was pushed a bunch of old fudds still saw jets as magical black-ops military stuff but that prop makes them look familiar.


text:
Does the FAA require a rating for night VFR?
Does a PPL require a specific rating or endorsement for night VFR in the US? Night flying seems like a special challenge and I'd think the FAA would want you to show that you've had proper training for it. This question talks about currency requirements, but I can't find anything on a night VFR endorsement.

I think it is worth noting that the Sport Pilot License does not include Night flight.   That is one critical difference between Sport and PPL.

There's no separate night rating or endorsement in the US, it's included in the private pilot flight proficiency requirements (14 CFR 61.107) and the specific required experience is in 14 CFR 61.109:

(2) Except as provided in §61.110 of this part, 3 hours of night
  flight training in a single-engine airplane that includes—
(i) One cross-country flight of over 100 nautical miles total
  distance; and
(ii) 10 takeoffs and 10 landings to a full stop (with each landing
  involving a flight in the traffic pattern) at an airport.

Some very minimal instrument training is also required, which can be helpful at night:

(3) 3 hours of flight training in a single-engine airplane on the
  control and maneuvering of an airplane solely by reference to
  instruments, including straight and level flight, constant airspeed
  climbs and descents, turns to a heading, recovery from unusual flight
  attitudes, radio communications, and the use of navigation
  systems/facilities and radar services appropriate to instrument
  flight;

That all applies to private pilots; sport pilots may not fly at night. And as David pointed out, there is an exception to the night requirements under 61.110 for pilots in Alaska: they can skip the night training but if they do, they can't fly at night.

So it's just part of the PPL but has a separate currency retirement?

@TomMcW It's part of the PPL but the currency requirements are only for carrying passengers, there's no currency requirement for flying solo at night (apart from the general flight review that's required every 2 years).

Also realize regulatory currency is different from Insurance requirement currency, which for small GA planes and flight clubs is usually 30 days otherwise have to go up with an instructor to fulfil the currency requirements.

You can obtain a PPL without meeting the night requirements in Alaska. You will have a special limitation that prohibits flying at night. See 14 CFR 61.110. You can get that limitation removed by convincing a DE that you have had the required training.

@DavidSchwartz Thanks! I've updated my answer. Alaska always has to be different :-)

I think Alaska is different because at certain times of the year (simmer) there is very little true night.  Deep twilight is the darkest it gets anywhere near the Arctic Circle.

@PJNoes: Of course, at other times of the Alaskan year, there is very little that isn't true night, at which times a daytime-only private pilot might find things a bit difficult.


text:
What is "Director" in ATC?
On this question SentryRaven gave the following list of ATC stations:

Delivery (if available)
Apron/Ground (if available)
Tower
Departure (if available, sometimes handled by Approach)
Enroute ACC/Center (multiple stations along the route)
Arrival/Approach
Director (if available / in use)
Tower
Ground (if available)

I am not familiar with Director. What does this ATC position do and when is it used?

there's also "ramp control" at many US airports, which is different than ground. for example, at KMIA:
RAMP CONTROL AT 305-876-7550 AND UPON ARRIVAL ON FREQUENCY 131.600
http://www.airnav.com/airport/kmia

Ramp control is not considered an ATC position. They aren't staffed by air traffic controllers

Some TMA arrival sectors can be further split up into an arrival/pickup part and a director/feeder part.
The arrival controller is responsible for getting aircraft separated either onto downwinds or onto transitions, where they are handed off to the director. The director is then only responsible for turning these aircraft onto the approach, in most cases the ILS.
Essentially, the arrival or pickup tries to get everyone onto the correct separation and speeds, so the director or feeder can turn and clear the aircraft onto their approaches, i.e. feeding the ILS with aircraft.

(Source: SentryRaven - Own Work)
The above picture shows the TMA airspace of Frankfurt (EDDF). The TMA arrival controller would clear aircraft onto the transition or a vectored downwind (indicated in red) and hand them over to director.
The director position would then vector the aircraft onto the ILS (indicated in green) for a handoff to tower.

It must require a phenomenally busy airport to require three controllers to handle such fine pieces of the approach and landing sequence.

@FreeMan Nearly every larger international airport has a director/feeder position and frequency available on stand-by somewhere. Check the AIPs, you will find a frequency listed... ;)

IANAP (Not A Pilot), didn't know that. Learned something new! But, then, that's what I come here for. Thanks!

That's a lot of handoffs! Keep the PNF busy!

@FreeMan As here in Germany the Stations are staffed with 2 people it's actually 6 controllers :) And in Frankfurt we have up to 16 people at 8 stations working at the arrival/departure sector.


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Why would a VOR be decommissioned leaving the DME?
As can be seen on this question and this question the OJC VOR has been decommissioned but the DME is still active. What would be the purpose in having DME without VOR?

OCJ is directly short of a runway, so the DME could still be useful in combination with the ILS.

With 3 distances from a DME you can know exactly where you are on a 2D map (in contrast with only 2 from a VOR and 1 from a VOR+DME)

FMS can use DME DME for position update as DME is more accurate. VOR is not used

Many older Air Transport Airplanes have no GPS. I'm a pilot since 1970. I operated A330 for 5 years until 2000 without GPS. The average IRS position (Inertial Reference Systems) in the FMS was updated by DME/DME. On older airplanes we selected the DME Stations manually preferably with a 90 degree cut-angle to obtain an accurate update. A single VOR/DME station could be used for update as well but it's a lot less accurate. Example, if you are 60 NM away from a VOR, a 1° error in azimuth would cause an error of about 1 NM. All Airbus aircraft have an approval for RNAV Approaches down to an accuracy of 0,3 NM with 2 DME stations available. This is why DME's are still useful, many ILS have a DME. Conventional VORs are terribly inaccurate, Doppler VORs are much better even down to a lower altitude, but requires more space.

I never realized dme had so many uses as a standalone device. And welcome to aviation.se. We get a lot of airbus questions here and i don't think anybody else on here has flown them. It'll be nice to have your pov.

authors: Наталья Чусовитина


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Why isn't the point you begin descent part of the flight plan?
In This question there is discussion about how to determine when to start the descent from cruise. There are several factors at play and it is usually calculated for maximum fuel performance.
Would this calculation not be done ahead of time, especially for aircraft cruising in class A airspace (presumably by dispatch for part 121 ops)? Why is this not included in the filed flight plan? Wouldn't ATC want to know when to expect this, especially if you lose coms?

For most of my professional flying I don't file, but I also don't have a descent point. I usually have to ascend to arrive at pattern altitude.

You can calculate ToD beforehand or let the FMS do the work.  In reality though, you generally don't get to wait until your optimal ToD to start descending, especially flying into busy airports.  If the airport has arrival routes, you'll be flying one and there will be crossing restrictions that are either part of the arrival clearance or expected clearances from ATC.
When you are flying the route you'll set the crossing restriction altitudes in the FMS and the FMS will generate ToD points to make those restrictions.  You can also use the 1000' / 3NM rule to calculate your own ToD for each crossing restriction.
Going into smaller fields I often set my own target altitude of 10,000' 30 NM from the airport and used that to generate a ToD for descending from cruise.  If you are landing in the direction of your arrival into a small airport and ATC is generous with pilot discretion descents you can sometimes manage an idle descent from cruise all the way to the FAF, but not often.
Finally, while the ToD might not explicitly be on the flight plan, it is accounted for in the planning.  The dispatcher has to account for expected fuel burn for the flight so we have the right amount of fuel, and the performance calculations they do takes the descent from cruise into the terminal environment into account.

Because the Top of Descent (TOD) is calculated in flight based on current weather data, STAR/Transition assigned, directs received during the cruise portion of the flight, vectors received taking you off your planned route, etc.. The FMC does the calculation for you with higher precision in flight.
For regular ops, ATC can use the rule of thumb 10.000ft / 30 NM to calculate an estimated TOD. In most cases, they will not need to do that however, as they can give instructions to aircraft to plan a certain STAR entry gate at an assigned flightlevel/altitude.
R: DLH123, when ready descend FL240 to be level\to reach at ARPEG
During lost comms, you are expected to maintain your filed or last assigned flightlevel/altitude until you reach the clearance limit. From there you will begin your lost comms procedures which usually include holding at the Initial Approach Fix (IAF), descending at the IAF to the approach altitude, and commending the standard approach procedure for the active runway.

So you stay st cruise alt until the IAF then descend in a hold?

Essentially, yes. [Leaving a clearance limit:
Fix from which approach begins (IAF): commence descent or descent and approach as close as possible to the EFC time if one has been received, or if one has not been received, as close as possible to the ETA as calculated from the filed or amended (with ATC) estimated time in route (ETE)](http://www.cfinotebook.net/notebook/flight-hazards-and-safety/lost-communication)

@TomMcW See also here: http://studentpilot.com/interact/forum/showthread.php?19259-Descending-and-Lost-Comm-Procedures

There is exception, based on jurisdiction. In Germany, the route terminates at the STAR or transition entry fix. This is also your clearance limit, so you would begin the descend there to the published altitude in the STAR or transition charts. Then from there you would hit the IAF (or fly the transition) and descend with the segments.

So, basically, there are just too many unknowns to calculate TOD ahead of time?

I think maintaining cruise till the IAF will be very rare except in busy airspace. I have never experienced it. Have you? The link you provide is exclusively for lost comms.

@JonathanWalters Well usually you are cleared to be at the correct altitude at the IAF or you are vectored around anyway. But when there is no other instructions and you are in lost comms... you maintain altitude until the IAF.

@SentryRaven Are you speaking from real world experience?

@JonathanWalters Yes. What else do you want to do? Start your descent in lost comms with ATC having no clue what you are doing? That's why there is lost comms procedures :D

I was under the impression that the STAR or transition was part of the flight plan. Is that assigned later by ATC?

This is only true for some countries, in Germany you are required to file SID and STAR, in other countries it's not required or not even asked for, because it's ATC assigned at startup.


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Why are the fan blades mounted loosely?
In this question it is mentioned that the fan, compressor and turbine blades are mounted loosely in the disc. This is well demonstrated by this video posted by RedGrittyBrick.
What is the reason for this?

@mins I'll add that in, but it does apply to compressor and turbine blades also. The turbine blades have even more play to allow for thermal expansion.

The blades are loose in their "Fir Tree" blade mounts so that they can self balance. They are called "fir tree" because they are v shaped.
As the rotation speed and centrifugal force increases, they move in the mounts and establish individual lead/lag positions to achieve a balanced disc.

It will be understood that turbine wheels rotate at very high speeds
  of rotation, thereby generating large centirfugal forces tending to
  throw the blades outwardly from the wheel. By providing contact
  surfaces of equal and opposite slope with respect to the longitudinal
  axis of the root on opposite sides of root, the force components of
  the centrifugal force balance each other out. Periodic and other
  vibrations which might otherwise be generated are damped out and
  greatly minimized

Source: Fir tree blade mount Patent

I would suggest to add to the description that having them loose is reducing the maintenance cost, and as having the centrifugal force ensuring they are connected to the rotor it is more efficient this mounting

Going to take some effort to wrap my head around how that works. So if a blade is a tiny bit heavier than the rest it will rock forward some to compensate?

I's like to expand the answers on how this could reduce vibrations, as it was mentioned in a comment.
Therefore, I'd like to look at something completely different: When computers were equipped with faster and faster CD-ROM drives, the reduction of vibrations caused by small imbalances in the discs became more and more important. The solution is is shown below. The spindle which sets the CD into rotation contains a circular shaped grove with a few metal balls, which can move freely in the grove. It looks a little like a ball bearing which lost some balls:

(Source)
Let's consider there are just four balls. If the disc  is perfectly balanced, the balls will arrange themselves so that all centrifugal forces (black arrows) point away from the axis of rotation and cancel out each other. The center of gravity (COG) is located on the geometrical center, which is also the axis of rotation:

Now let's consider some imbalance, modeled as additional mass here, which will shift the COG away from the geometrical center towards this mass (My library put barcode stickers on their CDs...)

If the disc could rotate freely, it would rotate around its new COG.
If the support of the spindle is absolutely rigid, it forces the disc to rotate around its geometrical center, though the imbalance exerts a centrifugal force and heavy vibration on the support.
If the support is flexible, it will follow the centrifugal force of the imbalance at low RPMs. (Left animation)
At higher RPMs, something strange happens: The spindle starts to act as counterbalance for the imbalance, and the disc rotates around a point between the COG and the geometrical center. Yet, the movement of the spindle exerts forces, i.e. vibration on the support. (Right animation)

This is a resonance effect and a bit hard to understand. Maybe, an analog: Hold a spring with a weight at the lower end. When you move your hand up and down slowly, the weight will follow your movement exactly. But when you move your hand much faster than the resonance frequency of the system, your hand an the weight will always move in opposite directions. (I guess, this still does not make it clear, but I have no better explanation...)
However... What happens to the balls?
I have drawn the centrifugal forces (black) on the four balls in my last point / right animation:

The disc rotates around the green x instead around the geometrical center (red +). The centrifugal forces point away from the green x. With respect to the geometrical center, the force on the upper and lower ball can be dissected into a radial (gray) and tangential (magenta) component. As the balls can move freely in the grove, they will follow the tangential force to the right. This means, some mass shifts from the left to the right side and as consequence, the COG and the axis of rotation are  much closer to the geometrical center.
Finally, this principle can eliminate the vibration to a large extent.
Coming back to a fan, the loosely mounted blades act like the balls. As the fan is for sure already well balanced, it is sufficient if they can just tilt a little in their position.

In the tangential force caused by the vibration?

The fan wobbels, i.e. it rotates around the green x, which also is the origin of the vibration. The tangential force is just the dissection of the centrifugal force (black). So, the wobbling causes vibration and this force.

Very nice explanation. This must be the same principle behind the little plastic beads they put in motorcycle ties to balance them

Fantastic post.

There are a few reasons for assembling the blades loosely in the gas turbine engine.

The loose attachment of the fan blades allow for the easy installation/removal of the fan blades.
Though the blades are loose while the blades are stationary, as the engine start spinning, the centrifugal force pushes the blades out and as a result, they will not be so loose. Still, the blades can move slightly in their attachments in order to dampen the vibration.
Another thing is that the blades (especially turbine blades) undergo thermal expansion, in which case they may warp if there is no space for expansion.

You need to realize just how big the radial force on each blade (caused by the rotating shaft) actually are, when the engine is running at in its normal operating speed range. Those centripetal and centrifugal forces are literally thousands of times the weight of the blades. On each fan blade of a large turbofan engine, the radial load on the blade root is more than 100 tons (or tonnes, for non-US readers).
There is no practical way that you could clamp up the blades with forces as large as that when you assembled them, even if there was any point in doing so. It's more sensible to design the fan so that is easy to assemble, and let it clamp itself rigidly when it is operating. The only disadvantage is that if the rotor is turning very slowly, you can often hear individual "clicks" from the blades moving about as they rotate, which can frighten the uninitiated.


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What in-flight weather info is available to commercial pilots?
This question was asked yesterday about sources of wx info. The answers focused on sources for pre-flight planning. As weather changes constantly pilots need current wx info en route, especially on long flights.
The wx radar aircraft are equipped with can show what they are approaching for the next several miles, but often pilots need to know what is in their path much further ahead than what onboard radar can show.
This question asks about in-flight wx info via cellular connection. The answers all allude to the unreliability and possible illegality of cellular use. However, in the comments several people suggested sources available through satellite and FIS-B.
I was reading this blog post relating to the recent Delta flight which suffered severe hail damage after flying into a storm. The author decries the lack of weather info sources available to commercial pilots in-flight. He says, "a pilot flying a single engine Cessna 172 can have significantly more weather information available to them in the cockpit than the crew of this A320 had." The author of the blog post is advocating for airlines to provide this info.
With many airliners now equipped with wifi it seems a pilot could have access to any number of ground-based NEXRAD radar services through a tablet or their EFB. What is there preventing commercial pilots from using these services? Is there an FAA rule that prohibits this or do airlines have rules as to where they can get their weather info?

Air Traffic Control
Air Traffic Control (ATC) are often a major source of weather information for pilots. Modern ATC radars often overlay weather radar over the screen so ATC can assist pilots in avoiding weather. In terminal areas ATC may be equipped with additional systems such as terminal doppler weather radar (TDWR) or low-level windshear alert system (LLWAS). If able, ATC will impart any weather information they have to pilots to assist them in choosing the safest course. That's an ideal scenario of course and sometimes ATC isn't helpful.
En Route Flight Advisory Service (EFAS or Flight Watch)

A service specifically designed to provide timely en route
  weather information upon pilot request is known as the en
  route flight advisory service (EFAS), or Flight Watch. EFAS
  provides a pilot with weather advisories tailored to the type
  of flight, route, and cruising altitude. EFAS can be one of
  the best sources for current weather information along the
  route of flight.
A pilot can usually contact an EFAS specialist from 6 a.m. to 10
  p.m. anywhere in the conterminous United States and Puerto
  Rico. The common EFAS frequency, 122.0 MHz, is established
  for pilots of aircraft flying between 5,000 feet above ground
  level (AGL) and 17,500 feet mean sea level (MSL).

Hazardous Inflight Weather Advisory (HIWAS)

Hazardous Inflight Weather Advisory (HIWAS) is a national
  program for broadcasting hazardous weather information
  continuously over selected navigation aids (NAVAIDs). The
  broadcasts include advisories such as AIRMETS, SIGMETS,
  convective SIGMETS, and urgent PIREPs. These broadcasts
  are only a summary of the information, and pilots should
  contact a FSS or EFAS for detailed information. NAVAIDs
  that have HIWAS capability are depicted on sectional charts
  with an “H” in the upper right corner of the identification
  box.

XM
Many modern avionics systems receive NEXRAD over XM as well as a myriad of other weather sources. Avionics suites such as the Garmin G1000 give pilots access to NEXRAD overlay over a map as well as a visual display of METARs, TAFs, FDs, PIREPs and many other weather information sources. There were a lot of acronyms there, but they can all be referenced in the two references provided at the bottom of this answer.
On-board Radar
Many aircraft are equipped with radar on-board. This provides a major step up from NEXRAD for making specific choices. Some pilots may disagree, but I view NEXRAD as a way to make "overview" choices about weather. NEXRAD is often too far delayed or affected by errors to make fine-grain choices. On-board radar can be directed at the airplane's altitude and provides an immediate picture of what's happening.

I also read the article from ForeFlight about the Airbus that got into hail. It's true that many general aviation aircraft have more in the cockpit that airliners. I'm not sure if airline pilots are allowed to use additional sources from things like ADS-B receivers they bring with them, but my guess is that while it's probably not forbidden, it's a risk to the pilot. If a situation arose where a pilot made a decision based on information from an unofficial source and it lead to a bad result it could be detrimental for the pilot and the airline. Most pilots probably stick to their official sources.

For pilots flying under the FAA, two good sources for the answer are the Pilot's Handbook of Aeronautical Knowledge (PHAK) Chapter 13 and AC 00-45G. Chapter 13 of the PHAK is dedicated to aviation weather services, many of chich are available in flight. AC 00-45G is dedicated to the same, it just tends to be updated a little more often and goes into greater detail.
Generally speaking though I have found that FAA materials haven't done the best job in keeping up with the fast pace of technology and its modernizing effects on avionics. Then again, the modern technologies are usually repackaging existing weather services and providing them in a better interface.


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How are fan and compressor discs balanced?
@curious-cat brought up an interesting question on another thread. How are the fan discs, compressor spools and turbines balanced on a jet engine. As they wear they surely get out of balance. Do they add weights as is done on your car tires?

And what method do they use to determine where the balance point is?
I'm imagining a giant version of this

Not an actual answer but, there is a youtu.be channel called agent jayz and he maintains industrial jet turbines and make videos about them. One of the videos he talked about balancing but couldn't recall which video it was

This article covers the issue (and is a pretty interesting read) but does not really explain how they do it. It just says

After machine balancing, the part can then be manipulated (mass added
  or removed) and retested on the machine until satisfactory balance
  tolerance is achieved.

In answer to this question,

And what method do they use to determine where the balance point is?

The device is pretty similar to that of a tire balance, here is a video of one in use and here is an interesting sales brochure for one.

"tooling must repeat to 0.000028 in, or about three-quarters of a micron." Holy $@*+! That's smaller than bacteria! Heck, the pandora virus is larger than that!

Im trying to find some documentation on how the blades are balanced but cant really seem to find anything.

As a 25 year gas turbine veteran across many different engines, including engine strip and assembly, it goes like this - The discs and blades are balanced independently to start with. The disc/hub arrives pre balanced, the technician then has to make a set of blades up with roughly similar weight. Each blade's weight is then inputted into a programme which spits out a plot of what blade is situated where on the disc. Once built the disc is then spun in a balance machine to make sure everything is in tolerance.
Large fans are generally balanced on wing using test sets etc.
They don't 'wear' as such as they don't touch anything, picking up deposits, damaged and subsequently blended blades etc might put an out of balance component in there but that's about it. Unless catastrophic damage occurs they're generally in there until the life runs out.

Welcome to aviation.stackexchange! This sounds like you are working on jet engines. Could you provide a reference for this or mention your personal experience?

I'm an ex Royal Air force aircraft tech, who spent 5 years building engines, mainly turbines and hot end modules, I now work for Rolls Royce as a field service tech.

Good to have another expert on this site! You might want to mention this at the beginning of the answer, people tend to trust an expert more than a random stranger on the internet ;)

There we go, done :)


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Do IFR flight plans ever get rejected for operational reasons?
I'm not talking about errors or omissions. Does a FP ever get rejected for example if there are too many flights scheduled into an airport or it conflicts with other flights or your FP as filed would take you through an active TFR area? How much scrutiny does a FP get when it's filed?
From this question I see that VFR plans get pretty much just filed away in case you need S&R. Does someone at ATC go through and verify that an IFR plan doesn't have conflicts?

Generally speaking, the only reasons for which a flight plan would be actually rejected would fall under what you referred to as "errors or omissions". But, the operational reasons you cite might lead to an amendment to your flight plan (which the pilot would most likely receive as an amended clearance).
IFR flight plans filed electronically are rejected by the flight plan processing computer if the filer files an impossible flight plan. I would presume that a flight plan filed verbally or in person through ATC or FSS would also be rejected for the same reasons, probably by the same computer, but with the rejection relayed to you through the third party. See these rejection examples that AOPA lays out in this article:

If you plan a "direct" flight, point-to-point, follow the rules and
  enter the correct equipment. For example, if "/G" (or "slash Golf,"
  meaning that your airplane is equipped with an IFR-approved GPS and a
  Mode C transponder) or "/I" (you have loran or VOR/DME and a Mode C
  transponder) are not entered for these kinds of flights, the air
  traffic control computer will reject your flight plan because that
  route can't be flown with less capable equipment.

and,

File fixes that are actually on
  the airways that you file in your IFR flight plan. Pilot error causes
  flight plans to be rejected when the filed points are not on the
  routes that are filed.

Depending on how you file, other possible rejection reasons might include formatting errors, a non-existent clearance limit, or might depend on the specific filing means; I am certainly not familiar with all means of filing. I have filed in person with a sheet of paper when standing in the office at the bottom of a control tower, over the phone, and online, and over the aircraft radio; I've never had an IFR flight plan actually rejected.
Beyond such reasons, a flight plan will typically not be rejected as such, but may well be amended. The reasons you propose—traffic density, route issues, etc—are usually negotiable, or are circumvented by amendments to your clearance. Certainly, these issues may present challenges, but they can usually be worked around.
These flight plans do receive scrutiny; IFR clearances are all about traffic separation, and this is ATC's primary task. Understand that to file an IFR flight plan is, essentially, to apply for a specific routing for specific time frame; you may or may not be given your requested routing when you receive your actual clearance. Receiving a clearance different from the route filed, or receiving a clearance amendment while en-route are both common. Note that an amendment need not be ATC initiated: the pilot can request an amendment, either before or during a flight.
One final note on TFRs: you can sometimes (often?) fly through these, even under VFR; you just have to get approval. For example, I've flown through the Grand Forks TFR while flying VFR with ATC approval.

@AIC12302 Such a flight plan should be accepted by the system and print a strip just like it would for any other flight. The system does not discriminate based on aircraft type. While uncommon compared to much larger aircraft, small prop aircraft do operate to and from such large airports. Often the landing and FBO fees encourage operators to consider options elsewhere.

@AIC12302 Approach control would have the job of finding a gap to fit you in for landing, and would use the option of having you orbit out of the way for 5-20 minutes until they could make the appropriate gap. Departure might be easier if tower immediately vectored you out of the departure corridor and kept you low. Using a separate runway might also be an option for either approach or landing. JFK, for example, often only uses two of four runways (in my limited experience). The closest I got to this scenario was flying pipeline patrol over busy airports where approach would just fit me in.

In busy airspaces like Europe and US east coast, checking for congestion is done. This does not mean directly comparing the specific routes and waypoints—conflicts on that scale are easily resolved by assigning different altitudes—but number of aircraft that are expected to fly through each sector, or land at each airport, at every hour. And only certain number is permitted so the controllers assigned to the sector can handle it.
But as far as I know the Network Manager Operations Centre (formerly Central Flow Management Unit; that does this in Europe) does not reject the flight plans, but it delays them. You file a flight plan and they'll give you expected release time. And if the destination or some sector along the route are congested, this might be several hours in the future. And then it's up to you whether you accept the wait or try to file a different plan that avoids the congested airspace. In airlines the dispatcher does this depending on how the extra fuel needed for longer route compares to the disruption caused by the delay.


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Why choose to ditch in the sea over bailing out?
I recently watched the film Dunkirk (I highly recommend watching it).
Without wanting to give away too much information about the film, a Spitfire pilot is flying over part of The Channel. They lose their engine and state the sea looks calm and opt to ditch over bailing out.
Why would a Spitfire pilot choose to do this? Is ditching in the sea really safer than parachuting out?

Maybe the pilot tryed to reduce the distance to the beach or a nearby ship?

Parachuting over water may have a lot of risks e.g. chute not deploying, getting tangled in the chute and drowning.

I thought he didn't bail because his canopy was jammed?

Bailing out the cockpit during that era was neither an easy nor always a successful task. The pilot had to either roll the plane, open the canopy, and release themselves to the void, or if rolling wasn't possible, walk on the wing and jump.
That's inherently unsafe. Don't forget that you are not exiting a healthy plane. There might be smoke, debris, fire, propellers spinning, the tail that might cross your way out.
Read what happened to Hans-Joachim Marseille when he tried to bail out. Quote from Wikipedia:

the left side of his chest striking the vertical stabiliser of his fighter, either killing him instantly or rendering him unconscious to the point that he could not deploy his parachute.

Now, regarding ditching versus bailing out, I don't have any source to substantiate the chances of survival, because in the end, what matters is to get out of there alive. But I guess it depends on many factors, one of them being the sea state as they mention in the film.
Another one is the type of damage the airframe has sustained. It might be better to risk a "gentle" contact with the water if there is no "urgent reason" to leave the plane and you can ditch reasonably soon, than to exit the cockpit and increase the chance of being injured by anything that I've mentioned in the first paragraph.
Finally, it turns out that the choice heavily depends on the situation. I haven't seen the movie so besides the "sea state" I don't know the details. So provided that you are above a water mass capable of supporting the ditching idea, the factors mostly influencing the decision are:

Airframe condition
Altitude below you as Pete pointed out and Philip Johnson mentioned in his answer. Too low and you might not have time to deploy parachute.
Sea state
Time of day. You might want to touch water at a lower speed if you can't see it.
Position of allied forces and/or shore. Surviving the crash is one thing; being rescued a whole other.

@Pete indeed and that's why I've edited to add a list of factors that could influence the decision making process.

+1 Good detailed answer, I'd also add, many a pilot successfully evacuated his aircraft and safely opened their chutes only to be killed by a strafing pass by the enemy aircraft as they floated down when they were a sitting duck. Unfortunately, killing the pilots was deemed more important. Aircraft could be replaced, pilots, not so easily.

@Trevor Thanks. And indeed this was a threat and it constitutes a war crime! But the article in Wikipedia mentions that most of the pilots were having second thoughts about practicing this, so I wouldn't add it for the sake of brevity :)

In The Big Show, Pierre Clostermann mentions another technique for bailing out of a low flying plane by unbuckling, pulling up and then pushing the stick away hard. That would be easier and safer than climbing out. Still, not necessarily safe, of course.

@Trevor I believe most pilots in WW2 didn't shoot at enemy pilots parachuting down, they didn't want the same to happen to them. You're more at risk of ground troops shooting at you, thinking you're part of a parachute assault (though the reverse also happened, Dutch ground troops failed to shoot at German paratroops, having been ordered not to shoot at pilots who'd jumped out of damaged aircraft).

In case of Spitfire, ditching in sea is not safer than bailing out. Spitfire XIV & XIX pilot's notes specifically states:

71 Ditching
(i) Whenever possible, the aircraft should be abandoned by parachute rather than ditched, since the ditching qualities are known to be very poor.

I don't think the advice would be any different in case of earlier models.
In such a case, the pilot's decision depends on his mental state under extreme stress. Maybe he was afraid of getting caught in the suspension lines of the chute, or hypothermia, which was quite possible if there is no timely rescue.
Or maybe he simply felt safer flying the aircraft than bailing out. It has to be noted that the pilots were not given any practical training in bailing out, which was hazardous at the best of times (even now with ejection seats). The description of a Spitfire pilot about bailing out goes like this:

... you loosened your straps, jettison the canopy and held the aircraft level, but trimmed forward and you let go the stick, which bunted the aircraft and you shot out and then the aircraft would drop away and as you dropped, you could pull your parachute...

No wonder the pilot preferred to be in the cockpit. This particular pilot forgot to jettison the canopy and his chute got caught in it, then escaped somehow and forgot to pull his chute before finally getting on ground in one piece. In that state, the pilot might have decided to take his chances rather than follow the notes.

Also, I've done ~1700 skydives and the lowest I've ever jumped out was ~2000 feet AGL. I have some friends who got special permission to jump from 1200 feet for a specific demo, but I really wouldn't to get out any lower than that - even with 'bad' ditching characteristics.

Military airborne operations are done well below 1200 feet.  Airborne school jumps are done at 1200, normal jumps are done at 800-1000 and real combat jumps are done at 500.  Those are static line, so if you were manually deploying your chute, you simply have no time for delay, and in the case of combat jumps, no time for a reserve deployment

Think it's worth noting that this is also a film based on true events. How true the events are is open to artistic license, and while the film is supposed to be a good film I haven't heard anything about the realism. So I wonder whether, if it was real, the pilot would've bailed but it makes a better cinematic scene if they ditch rather than bail.

Doing parachute training on static lines, the jump-master went through his speil as we took off, 'if there's a problem with the plane, and we're above 500ft, we just throw you straight out of the door!' Just what beginner wants to hear!

@mickburkejnr not sure about the realism but the historical accuracy is ... close to 0.

@simonatrcl "I really wouldn't [want?] to get out any lower than that" - but if you are in the military, you have already signed up to a deal that says the possibility of getting killed is part of the total employment package. Most civilians are in a different situation!

@alephzero: Yes, but I'd think even though ditching isn't ideal in a spitfire plenty of people did and survived.

@Antzi https://en.wikipedia.org/wiki/Dunkirk_(2017_film)#Historical_accuracy (not arguing one way or another)

@Kevin WW2 pilots didn't have static lines. And they no doubt had less overall parachute training than did paratroops.

I don't think WWII pilots had reserves @Kevin, if your chute was bad that was it.

@GdD I would assume they did not.  IIRC, they don't even use them on actual combat jumps, only training jumps, because you are jumping out so low, there's no time to deploy a reserve

@Kevin, there isn't enough room in the cockpit for a reserve, the chute is also your seat cushion. A reserve would have to go on your chest, a fighter cockpit is far too small for that.

Airplanes tend to float after ditching due to the air trapped in fuel tanks, wings and fuselage spaces, acting as a life raft which is very valuable. A ditched plane is also much more visible than a single pilot floating in the water, making rescue more likely.
The English Channel is also very cold throughout the year, being able to stay out of it by climbing on a wing will limit exposure and increase survival time dramatically. Spitfire pilots didn't have rafts, so this was an important consideration.

Even if the aircraft stays afloat, there is the hazard of the aircraft flipping over, coming to rest inverted, leaving the pilot submerged and trapped under his floating aircraft. I'd speculate this is the "poor ditching qualities" referenced in one of the other answers.

For baling out, height is the main criteria. If at a low height above the water there is a chance you will strike the water without the parachute being fully open, depending on the trajectory of the aircraft and the time it takes to get out of the cockpit.
Assuming there is enough height, I would have thought that ditching is more dangerous, because the impact forces could be high enough to knock the pilot unconscious against the gun-sight just ahead of his head, who will then drown when the aircraft sinks. Spitfires and Hurricanes were not known for floating for very long on the surface.
The procedure for ditching is not straightforward, but the whole aim is to minimize impact forces because these are a square of the speed (i.e. you double the speed you quadruple the forces felt), so its important to fly at the lowest controllable airspeed into wind (to reduce groundspeed) where possible but along the swell/waves so you don't crash headlong into a wave on touchdown. Try also to make the tail-plane the first thing that touches the water because the deceleration won't be as fierce as hitting wings or nose first. Also if its the nose or the wings first, on the Spitfire you could "submarine" (i.e. the flow of water over the wings would take the aircraft down before its even stopped). Undercarriage also must be up to prevent it making the aircraft flip or submarine on touchdown. Canopy open so it doesn't get damaged during the impact and then impossible to open quickly.
For whatever reason, in WW2 they were often feet underwater before the aircraft stopped moving so while you needed to be strapped in to survive the impact, you then had to unstrap pretty quickly and make your way to the surface.
I haven't seen the film, but based on the large number of WW2 biographies I have read, I think that in reality, given it is your own life on the line, and that you most likely haven't parachuted before, its entirely your own personal preference based on your own personal understanding and fears.
My personal view is that if you are doing much over 60mph in a small aircraft at touchdown in a ditching then the outcome is probably not going to be pretty, even 70mph may well make a big difference and 80 or 90 would most probably kill you. I'm not saying you can't survive higher speeds, but if you do then you are very lucky. You only have to read accident reports to understand that if you don't get the speed right, e.g. ditch downwind, or not at the minimum speed, you will be dead. This information only heightens my respect to the people who flew in wartime.

I know Captain Sullenburger survived a ditching at I think it was something like a 140 knot touchdown, but that was an airliner, not a Spitfire with a gunsight inches from your head. I think he went as slow as he could, got the tail in the water first and the engines managed to decelerate the aircraft without making the nose go under, and it wasn't damaged enough to sink immediately. So the above comment about 60mph doesn't apply. It was a combination of skill, luck and extreme coolness under pressure that saved Captain Sullenburgers day.

An A320 is not a "small" aircraft by anyone's standards. The stall speed of a heavy A320 (i.e.with a full fuel load) is, amazingly, (or not) about the same as Sullenburger's touchdown speed - somewhere in the range of 110 to 140 knots. The stall speed of some marks of Spitfire is as low as 40 knots, not 140.

I didn't say the A320 was a small aircraft... I kinda got ahead of myself when I was writing the bit about ditching and added the comment about the A320, then went back and adding SMALL aircraft in my main text because I was trying to be clear. Shouldn't have added the A320 comment I guess because it doesn't apply to this question. Oops!

So, a Supermarine would submarine?

In this very specific case, he was close enough to safe shores that the glide path provided significant benefit.  Ditching would allow him to get significantly closer to safety than jumping.
So looking at the short term, jumping may have been safer, but looking at the long term, ditching was seen as safer even once you account for the fact that ditching itself may be less safe than jumping.
No pilot decision is made in a vacuum, however, and as pointed out by many others there were many reasons for this decision that wouldn't necessarily apply generally or in other situations.


text:
How much are noise-related landing costs for a long-range aircraft at Heathrow?
I am trying to estimate the noise-related costs for a long-range platform aircraft (for example, the Boeing 787) at Heathrow Airport.
I have found the following table (PDF, page:24) outlining some costs for night/day landings, but can anyone tell me which 'chapter' a B787 would considered? I have looked around extensively, but cannot find any clear explanation on this.

Just FYI. This PDF shows the latest charges related to noise categories.

As DeltaLima states, the 787 is a Chapter 4 aircraft.
Directly under the table in your question is another table listing the requirements for each category.

So the categories are based on the certified Chapter, and the margin to Chapter 3 standards. Based on these values, the 787 would be categorized as Chapter 4 Low.
You can look up aircraft in the NoisedB here. Each aircraft is tested for its noise margin. I looked at ID:BOEING_14816, which is a 787-8 powered by a GEnx-1B. It has a noise margin of 30.9, which is compared to the Chapter 4 standard. From looking up a Chapter 3 aircraft like a 747-400, it can be seen that the cumulative reduction between Chapter 3 and 4 is 7.3 EPNdB. I did not see any aircraft that would be above the Chapter 4 Low levels, and most are in the "30 or more" category.

The B787 is a chapter 4 aircraft.
I don't know whether that would be chapter 4 'High', 'Base' or 'Minus'. These qualifications seem to be specifically used at Heathrow. I'd expect the B787 to be in the Base or Minus category since its noise levels are well below the ICAO
Chapter 4 standard.

do you have a reference for this standard? never heard (no pun intended) of it.

@Federico References here and here


text:
What was the Vmca of the 2-engine 747 config the El Al 1862 crew faced, and could they have landed the plane at a corresponding Vref?
In the El Al 1862 crash, the flight crew lost control of their 747 in what basically amounts to an aggravated Vmca roll during approach after two engines detached from the aircraft, causing the loss of two hydraulic systems and damage to flight control surfaces on the right wing.
What was the actual Vmca of the aircraft in that damaged configuration though?  Further, if they had not been focused on trying to get down to a normal configuration Vref and instead sped back up as soon as they started nearing full control deflection, thus increasing their control authority, could they have gone around and then reconfigured partially for what would be an increased Vref, then landed the aircraft at that increased speed?  Schiphol has no shortage of runway, after all...

@jjack Not in general, you‘re right. But there are some examples where crew succeeded in doing just that, at least partially. The most successful example would be the 2003 Baghdad incident DHL crew who landed their damaged Airbus A300 without any conventional flight controls using only engine thrust modulation.

@jjack -- the key to dealing with an aircraft that's had its envelope altered by damage is to figure out what the plane can and can't do while still at a safe altitude (i.e. a controllability check).

Keep in mind that the crew was unaware that the engines had completely separated. Knowing the extent of damage to the aircraft may have altered their decisions. They were doing what was required to land with inoperable or damaged engines. Once they had slowed down, speeding back up was probably not possible. What precipitated the final loss of control was when the engines were throttled up. They already had asymmetric lift and reduced aileron effectiveness. The asymmetric thrust and resulting yaw moment is what pushed the roll beyond the control capability.

To try to regain altitude from that point would have also required a higher AoA. The lift difference would have become more pronounced the higher the AoA. So without the ability to use engines to speed up and ability to increase their AoA, they were headed down regardless of what they did.

@jjack I don’t know of such a statistic, I‘m afraid, but it probably could be easily compiled with a little research, as there only have been a handful of cases where commercial airliners were „reconfigured“ in a similar manner mid-flight.

The accident report says

2.4.2 Performance
An energy analysis was performed based upon altitude and airspeed
  data from the DFDR. It should be realised that this method does not
  allow extrapolation of performance capabilities in other conditions
  then those encountered during this flight. Based on this analysis the following conclusions can be made:

Marginal level flight capability was available at 270 knots and go
  around power with a limited manoeuvring capability;
At MCT thrust and 270 knots IAS there was no level flight capability;
Performance degraded below about 260 knots at increased angles
  of attack. Deceleration to 256 knots resulted in a considerable sink
  rate.

(my emphasis)
My interpretation is that it is not appropriate to define a Vref for a 747 in that configuration.

Glossary
Vmca = Minimum Control (air) Velocity. Min speed that directional control can be maintained. Vmca2 for two engines (critical and inboard on same side) of a 4-engine aircraft.
Vref = Speed required as the landing runway threshold is crossed at a height of 50 feet in landing configuration.
MCT = Maximum Continuous Thrust. Thrust levels higher than this can only be maintained for a short time (e.g. minutes).

It also means that basically, there isn’t any excess energy available at TO/GA power (takeoff/go-around), so that there is no real chance of accelerating once too slow, and also no chance of attempting a go-around if the approach fails.

@jjack On the aircraft I am familiar with (mainly Airbus and Boeing), it is selectable by crew.

"Thrust levels higher than this can only be maintained for a short time (e.g. minutes) without risking damage to the engines" would be more accurate.


text:
How did old autopilots work?
With fly-by-wire and computers between pilot's command and flight control surfaces, it is easy to imagine the implementation of an autopilot inside the computer, but I read somewhere that autopilots existed before WW2. They were made only to maintain altitude and heading, but worked at a that time with the mechanical linked between pilot and control surfaces.
How did these old autopilots work?

"Clockwork" nav teardowns: 1 2

Well, Wilbur borrowed a pair Orville's suspenders, and tied them to the wheel....

Have to add a note: doing a google image search for suspenders autopilot is NSFW, at least at my work site.

The autopilot controls hydraulic actuator that is connected to the control link at some point. Since power transfer in the link is bidirectional, the control column moves when autopilot operates it. The same goes for thrust levers operated by autothrust.
If the pilot fights it, the autopilot will increase the force applied up to some limit at which it will disconnect. It can't really recognize whether the force is from the pilot or due to aerodynamic forces, but that's all right, because it should disconnect both if the pilot tries to yank the controls and when keeping the plane in the selected attitude requires too large control input (e.g. hard up elevator because the plane is too slow).
Boeing aircraft maintains this behaviour even on models with fly-by-wire (B777 and B787). Airbus did remove the feedback, because the command given does not directly correspond to control surface position anyway. So far I believe the only other civilian aircraft without feedback is Sukhoi Su-100.

Nothing personal, but I'm not sure why this is the accepted answer. While the information is valid, it doesn't seem to answer the question of how mechanical autopilots work.

@freeman the description states the OP (me) asks for the implementation of autopilot's control suggesting an explanation on interference with pilot's command.

It used a set of gyroscopes and pendulums that would correct the plane's attitude when it deviates. They were usually enhanced with pneumatic or hydraulic power to actually move the control surfaces.
For example the V-1 flying bomb (WW2 German UAV) could fly across the Channel and initiate a dive after a preset distance. It remained on course using a pendulum for pitch control and a gyroscope for yaw control. It used its inherent stability for roll control (no ailerons).

Does that mean that the pilot see the control moving and then can be harmed? Does he have to force if the autopilot does not disconnect?

@ManuH: Both autopilot and pilot move the controls gently. So he can see, and feel, them moving, but won't be harmed.

In airplanes without hydraulic actuators on the primary flight surfaces an autopilot usually consists of servos and a computer.  The servos lock onto the cables that control the primary flight surfaces.  When the autopilot moves the cable you can visibly see the control yoke move the proper amount.  It is not fast and will not cause damage.
The computer is monitoring the pitot/static instruments through the associated air data computer and the gyroscopic instruments through the associated attitude/heading reference system. Through algorithms, the autopilot computer controls the airplane.

This answer does not really answer the question either.